1. Field of the Invention
The present invention relates to semiconductor manufacturing devices and methods of removing foreign matters or particles therefrom, and particularly, to a semiconductor manufacturing device capable of reducing fine particles floating in a process chamber of the semiconductor manufacturing device and a method of removing the particles.
2. Description of the Background Art
Recently, development of electronics is conspicuous, which has largely depended on the technological advancement in manufacturing technique, including advancement in devices for manufacturing semiconductor devices. In a wafer process including a series of steps for forming a semiconductor device from a silicon wafer, a semiconductor wafer (hereinafter simply referred to as "a wafer") is processed in a variety of semiconductor manufacturing devices and completed as a product.
As the degree of integration of the semiconductor devices has been increased, processes for fine patterns are required. Accordingly, how to keep the wafer in wafer processing clean has become one of the major objects, and particularly, the need for a semiconductor manufacturing device having less particles has increased.
As an example of such a semiconductor manufacturing device, a dry etching system for processing a wafer in a vacuum will be described with reference to the drawings. Referring to FIG. 7, a lower electrode 20 as a sample stage is formed in the lower portion of a vacuum process chamber 10. Lower electrode 20 and vacuum process chamber 10 are electrically insulated by an insulator 11. A wafer 50 is placed on lower electrode 20. A high frequency (for example of 13.56 MHz) power supply 23 is connected to lower electrode 20 through a blocking condenser 22 for generating bias and through a high frequency matching circuit 21. An upper electrode 40 is also formed opposite to lower electrode 20 in vacuum process chamber 10. A supply opening 42 is formed on upper electrode 40 which blows off the gas supplied from a supplier 41 for supplying prescribed gas. Vacuum process chamber 10 is evacuated by an evacuation exhaust port 12 connected to an exhaust unit (not shown). In addition, a pressure gauge 13 for measuring pressure in vacuum process chamber 10 is provided through a pressure gauge portion 14.
An etching operation using the above mentioned dry etching system will now be described. Referring again to FIG. 7, wafer 50 which has been transported into vacuum process chamber 10 by a handling system (not shown) is placed on lower electrode 20. Then, etching gas is flowed into a discharge space 30 through a supply opening 42 from supplier 41. The pressure in vacuum process chamber 10 is controlled to a prescribed level by pressure gauge 13 and an exhaust conductance controller (not shown). After the pressure control, high frequency power is applied to lower electrode 20 by high frequency power supply 22. Thus, glow discharge occurs between lower and upper electrodes 20 and 40. Etching gas in discharge space 30 is excited into plasma 31 by the glow discharge. When the surface of wafer 50 is irradiated with plasma 31, an etching process is performed.
In the etching process, component under etching of wafer 50 reacts with activated species in plasma 31. The reaction product evaporates, goes away from the surface of wafer 50 and spreads into discharge space 30. Finally, the reaction product is discharged from evacuation exhaust port 12. At this time, part of the evaporated reaction product may experience polymerization reaction or the like and is solidified in discharge space 30. In addition, part of the evaporated reaction product may be cooled on the wall surface of vacuum process chamber 10 and solidified again.
The reaction product thus adhered for example to the wall surface of vacuum process chamber 10 and solidified becomes thicker as the etching process proceeds, until it becomes a solid deposit 60. Solid deposit 60 is eventually removed off from the wall surface of vacuum process chamber 10 and externally discharged, or falls on wafer 50. The solid deposit on wafer 50 may hinder etching, resulting in decrease in the productivity of wafers.
On the other hand, most of the reaction products which have been solidified in discharge space 30 have fine diameters no larger than submicrons. These reaction products are charged by plasma or collided with neutral particles to form particles 70, most of which float in discharge space 30 for a long period of time.
Various proposals have been made as to removal of particles in such a vacuum process chambers, and more specifically, of solid deposition 60 which has been adhered to the wall surface of vacuum process chamber 10. In Japanese Patent Laying-Open No. 6-295882, for example, one method of preventing adhesion of reaction product is disclosed in which the wall surface of a vacuum process chamber is heated above the evaporating temperature of the reaction product by a heater or the like. In addition, a cleaning method by means of plasma has been generally adopted.
The removal of the particles in the above described dry etching system, however, suffers from the following problems.
It has been reported that there exists such a relation between the size of the particle which affects yield of wafers and a design rule, as shown in FIG. 8. According to the relation, a particle having a diameter of around 0.1 .mu.m would affect yield of 1 G-DRAMs, the production of which would begin around the year 2000.
Meanwhile, there exists such a relation between the size and the number of the particles generally existing in a certain space, as shown in FIG. 9. According to the relation shown in FIG. 9, it is apparent that the particles having smaller diameters are larger in number. It is known that a fine particle in particular floats in the space within a vacuum chamber for a long period of time even under a depressurized state as in the atmosphere, once it is produced. This is now explained in detail using the drawing. Artificial particles having diameters of 0.3 to 2 .mu.m are introduced into an enclosed space, and the relation between the time after stopping the supply of the particles and the number of particles existing in the space is obtained by a particle counter. The result is shown in FIG. 10. According to the result, under atmospheric pressure (760 Torr), there was not a large decrease in the number of the particles relative to the time elapsed after the stop of supply. On the other hand, under the depressurized state (12 Torr), while the number of the particles decreased as time passed, the particles could float in a space at least for 20 minutes. Accordingly, it is estimated that the particles having diameters of about 0.1 .mu.m, which is smaller than the minimum diameter of the artificial particles, would float in the space for a longer period of time.
Such fine particles cannot have been effectively removed by the conventional method of removing mainly the particles on the wall surface of the vacuum process chamber. In addition, fine particles have often been produced in removing the particles on the wall surface, disadvantageously increasing the number of the particles floating in the vacuum process chamber.
The operation of the dry etching device may also be stopped and manually cleaned. In this case, however, though almost all of the fine particles can be removed, uptime ratio of the dry etching device and hence productivity decrease.